Willy Rosenstein was a World War I ace and a pre-war aviation pioneer. He was born in Stuttgart on January 28, 1892. Because he had a keen interest in engines and cars, he decided to become a motor engineer. In 1912 he earned his pilot's license (No. 170) at the famous flying school at Johannisthal. Soon afterwards he became a flight instructor, a test pilot, and a contestant in airplane competitions. His great flying talent made him nationally known. When war was declared in 1914, Rosenstein volunteered for duty as a pilot. At first he piloted two-seaters: while he flew the plane, another man would observe the enemy below. Later in the war the observers were armed with machine guns and participated in air combat. Pilots of one-seaters had both jobs of flying and shooting, and Rosenstein eventually became the pilot of a one-seater. From February to December 1917, Rosenstein was a member of Jasta 17, which was under the command of Lieutenant Hermann Goering. (Jasta was short for Jagdstaffel, or squadron. It was part of a Jagdgeschwader, or wing.) Rosenstein had his first confirmed aerial victory while in Jasta 17. In late 1917 an incident occurred in which Rosenstein became very upset after Lt. Goering made an anti-Semitic remark in front of several people; Rosenstein requested an apology but when Goering refused, Rosenstein asked for a transfer out of the unit.

In Rosenstein's official assessment, Goering wrote that Rosenstein was a fine pilot but that he was suffering from nervous exhaustion, and for a short while Rosenstein was assigned border duty. He eventually was transferred to Jasta 40, led by Lt. Carl Degelow, and Rosenstein flourished under his command. Rosenstein shot down several more enemy aircraft and was even made Deputy StaffelfŁhrer (squadron leader). Rosenstein always received excellent assessments from Degelow. Rosenstein received credit for shooting down seven enemy aircraft (shooting down five or more made you an "ace"), but he most probably deserved credit for two additional victories. His last two victories occurred near the end of the war and as a result, his claims were never officially processed. Among the decorations he received for his wartime service were the Iron Cross (First Class), the Order of the Zahringer Lion, and the WŁrttemburg Service Medal in Gold.

After Hitler came to power, Willy Rosenstein found it difficult to fly. The Nazis made it very clear that he was not welcome at any flying fields. An old war comrade was in charge of one of the flying fields, however, and he refused to comply with Nazi orders that Jews were forbidden to fly. He allowed Rosenstein to use the field whenever he wished, but Rosenstein became concerned that his old comrade would soon get into serious trouble, so he stopped going to the flying field. Rosenstein decided that he and his family should get out of Germany, and although the Nazis did not want Jews in the country, they made it increasingly difficult for Jews to leave. When German Jews tried to emigrate, the government taxed so much of their money and property that in most cases there was not enough left to buy a passage to another country or to provide a means for making a living. Rosenstein was running into all kinds of Nazi bureaucratic roadblocks as he tried to leave the country. A man Rosenstein had barely known from his days in Goering's squadron told Rosenstein he would inform Goering of his dilemma. Considering the circumstances under which he had left Goering's squadron, Rosenstein expected no help. To Rosenstein's great surprise, Goering sent him a letter that he admits "made things easier in some ways," because he was allowed to leave the country and take three planes and their spare parts with him, "a privilege which was not granted to other Jews at that time [summer 1936]."